Your character doesn't need to purchase any additional skills to fly in Draenor, the Broken Isles, or Battle for Azeroth zones. However, you must earn an achievement to unlock the flying ability in each of these areas.

These achievements are Blizzard Account-wide but region locked. You can progress towards the achievements with all characters in your Blizzard Account on one region. Once you earn the achievement in one region, all characters in that region will be able to fly.

No-fly zones

Most instanced content is a no-fly zone (scenarios, dungeons, raids, battlegrounds, and arenas). There are multiple open-world no-fly zones as well: